Hola, Zachary. It depends on the country, really. In Chile, niño and niña are for boy and girl respectively, while chico and chica mean small (masculine and feminine). In other countries like Argentina it can mean kids any age or even boyfriend / girlfriend. But, again, it depends on the country, I'm sure it's used differently in other Latin American countries. I hope it was helpful. If you need any more information feel free to contact me :) Nos vemos!